Highly efficient gallium nitride based light emitting diodes via surface roughening

Abstract

A gallium nitride (GaN) based light emitting diode (LED), wherein light is extracted through a nitrogen face (N-face) of the LED and a surface of the N-face is roughened into one or more hexagonal shaped cones. The roughened surface reduces light reflections occurring repeatedly inside the LED, and thus extracts more light out of the LED. The surface of the N-face is roughened by an anisotropic etching, which may comprise a dry etching or a photo-enhanced chemical (PEC) etching.

What is claimed is: 
     
       1. A device, comprising:
 a gallium nitride (GaN) based light emitting diode (LED) including at least an n-type layer, an emitting layer, and a p-type layer; 
 wherein light from the emitting layer is extracted through a nitrogen face (N-face) surface of at least one of the layers of the LED, the N-face surface is roughened, and the roughened N-face surface extracts more light out of the LED by scattering or diffracting the light. 
 
     
     
       2. The device of  claim 1 , wherein the LED is grown on a sapphire substrate, the p-type layer's surface is a gallium face (Ga-face), and the n-type layer's surface is a nitrogen face (N-face). 
     
     
       3. The device of  claim 2 , wherein the N-face surface is prepared for roughening by a laser lift off (LLO) of the sapphire substrate. 
     
     
       4. The device of  claim 1 , wherein the N-face surface is roughened by an anisotropic etching. 
     
     
       5. The device of  claim 4 , wherein the anisotropic etching comprise a dry etching or a photo-enhanced chemical (PEC) etching. 
     
     
       6. The device of  claim 1 , wherein the N-face surface is roughened into one or more structures. 
     
     
       7. The device of  claim 6 , wherein the structures have a size close to a wavelength of the light within the LED. 
     
     
       8. The device of  claim 7 , wherein the structures have a size not smaller than a wavelength of the light within the LED. 
     
     
       9. The device of  claim 6 , wherein the structures comprise cone shapes. 
     
     
       10. The device of  claim 6 , wherein the structures comprise hexagonal shaped cones that have an angle equal to or smaller than:
   2 sin −1 (n air /n s ) 
 where n air  is a refractive index of air and n s  is a refractive index of the N-face surface. 
 
     
     
       11. The device of  claim 1 , wherein the extraction efficiency of the light out of the roughened N-face surface is increased by more than 100% as compared to an N-face surface that is not roughened. 
     
     
       12. A method, comprising:
 fabricating a gallium nitride (GaN) based light emitting diode (LED) including at least an n-type layer, an emitting layer, and a p-type layer; 
 wherein light from the emitting layer is extracted through a nitrogen face (N-face) surface of at least one of the layers of the LED, the N-face surface is roughened, and the roughened N-face surface extracts more light out of the LED by scattering or diffracting the light. 
 
     
     
       13. The method of  claim 12 , wherein the LED is grown on a c-plane GaN or sapphire substrate, the p-type layer's surface is a gallium face (Ga-face), and the n-type layer's surface is the N-face surface. 
     
     
       14. The method of  claim 13 , wherein the N-face surface is prepared for roughening by a laser lift off (LLO) of the substrate. 
     
     
       15. The method of  claim 12 , wherein the N-face surface is roughened by an anisotropic etching. 
     
     
       16. The method of  claim 15 , wherein the anisotropic etching comprise a dry etching or a photo-enhanced chemical (PEC) etching. 
     
     
       17. The method of  claim 12 , wherein the N-face surface is roughened into one or more structures. 
     
     
       18. The method of  claim 17 , wherein the structures have a size close to a wavelength of the light within the LED. 
     
     
       19. The method of  claim 17 , wherein the structures have a size not smaller than a wavelength of the light within the LED. 
     
     
       20. The device of  claim 17 , wherein the structures comprise hexagonal shaped cones that have an angle equal to or smaller than:
   2 sin −1 (n air /n s ) 
 where n air  is a refractive index of air and n s  is a refractive index of the N-face surface.